In recent years, liquid crystal display devices, which are a type of display device, have come into widespread use as display units in mobile electronic devices. For example, Patent Documents 1 and 2 disclose liquid crystal display devices having two display parts that can be individually displayed. The display device described in Patent Document 1 has a first display part that is a transmission-type liquid crystal display unit and a second display part that is a reflective-type liquid crystal display unit. In this display device, information that is to be displayed at all times, such as the time and date, are displayed on the second display part. Other information, such as characters and graphics needed temporarily, are switched between displayed and non-displayed on the first display part. Patent Document 1 describes this display device as being suitable for use in a mobile telephone, a portable computer, or the like.